HMRC doesn't publish a checklist of what triggers an enquiry, but some patterns draw more attention than others: figures that are out of line with your sector, income that isn't declared, and filing late or inconsistently. Keep your numbers clean and consistent and you're not the interesting one.
Here are the patterns worth understanding — and why HMRC often already has the data to spot them.
The patterns that draw attention
None of these is an official trigger, and none of them means an enquiry on its own. They're the kinds of thing that make a set of figures look like they don't quite hang together:
- Profit margins that are out of line with others in your sector.
- Expenses that look high for your level of turnover.
- A personal lifestyle that doesn't match the income you've declared.
- Income that isn't declared at all.
- Filing late, or inconsistently from year to year.
- Unusual cash patterns.
- Suspiciously round numbers that read like estimates rather than records.
HMRC often already has the data
Some of this HMRC can see without asking. Card payment processors report card-sales data to HMRC, and banks, platforms and online marketplaces report income too. That's how a gap between what's reported to HMRC and what you've declared can show up.
The point isn't to worry — it's that clean, accurate records are the thing that keeps the two matching.
How to stay off the radar
The good news is that staying clear of all this is ordinary bookkeeping. Declare your income, keep records that back up your expenses, use real figures rather than round estimates, and file on time and consistently. If your numbers tell a straightforward, consistent story, you're not the one that stands out.
Frequently asked questions
What triggers an HMRC investigation? There's no published checklist, but patterns that draw attention include margins out of line with your sector, expenses that look high for your turnover, undeclared income, late or inconsistent filing, and unusual cash patterns.
Does HMRC see my income automatically? In part, yes. Card processors report card-sales data, and banks, platforms and marketplaces report income, so a gap between that and what you declare can show up.
How do I avoid an HMRC enquiry? Declare all your income, keep records that support your expenses, use accurate figures rather than round estimates, and file on time and consistently.
Work with us
Keeping your records clean and your filings consistent is exactly what we take off founders' plates. Book a call with Carr Accounting Studio if you'd like that handled properly.
General information, not advice. UK rules 2026/27 — they change, and your situation may differ. Written by David Carr, chartered accountant and founder of Carr Accounting Studio.